Successful organ transplantation requires sustained immunosuppression. Currently, immunosuppressive treatment for cardiac allograft recipients is determined empirically. We have developed a sensitive and accurate technique to predict or confirm organ rejection and to discover if immunosuppressive treatment has modulated the immune response. Flow cytometric immune monitoring (FCIM) is a low-cost, sensitive, noninvasive assay which can detect opportunistic infections as well as predict transplant rejection. FCIM provides a scientific and rational basis for preventing rejection and diagnosing infection in the immunosuppressed transplant recipient. Cytometrics Laboratory has the capability to perform multiple marker analysis on peripheral blood lymphocytes for the identification of activated circulating lymphocytes. FCIM can be utilized to monitor all transplant recipients for rejection and infection. This research will lead to a cost-effective, noninvasive, sensitive tool to predict all transplant rejections.